Powered Up, Veteran Rover Soldiers Through Mars Winter

It may be fighting age-related issues, but Opportunity certainly isn't done with Mars yet.

For a rover with a prime mission of only 3 months, NASA's Mars rover Opportunity sure is going above and beyond the call of duty.

On Monday, the veteran wheeled rover celebrated its 12th year (yes, that's 12 Earth years, or 144 months) on the red planet and, although it's been a hard road for the robot, it is still doing science. And it's doing science during the most aggressive period of the Martian year, which is nearly 687 Earth days long.

PHOTOS: 12 Years On Mars: Opportunity's First Sols

On Jan. 2, the southern hemisphere of Mars dipped into winter solstice, marking the shortest, and therefore darkest, day of Opportunity's year. For a solar powered rover, this is not a fun time. Opportunity requires sunlight to charge its batteries, so when daylight is limited, rover drivers need to position the rover at an optimized angle to collect as much of the limited sunlight as possible.

But with its crazy-extended mission comes some frustrating issues. Primarily, Mars dust collects on solar arrays, further limiting the mount of sunlight that can be used to charge batteries. Only recently, mission engineers were growing concerned by the viability of the rover's solar panels; they'd become so encrusted in years of dust buildup that solar energy had slowed to a trickle.

Then, Martian Mother Nature stepped in and provided Opportunity with a wonderfully timed and much needed "cleaning event." Cleaning events have become a critical, yet unplanned component of long-duration solar powered missions on the Martian surface. Opportunity and sister rover Spirit have both experienced Mars winds and dust devils that have blown over the rovers, removing some of the dusty layer, giving them a power boost. Opportunity's most recent cleaning event occurred toward the end of 2015, before it plunged into Martian winter, thus allowing the rover to continue its valuable work into 2016.

VIDEO: Drive With Opportunity on Epic Mars Rover Marathon

"Opportunity has stayed very active this winter, in part because the solar arrays have been much cleaner than in the past few winters," said Mars Exploration Rover Project Manager John Callas, of NASA's Jet Propulsion Laboratory, Pasadena, Calif., in a NASA news update.

Since landing on Meridiani Planum on Jan. 24, 2004, Opportunity has provided some huge clues to Mars' ancient wet environment, the planet's unique geology and atmospheric dynamics. Having an unexpectedly long-duration rover on Mars has also taught NASA a thing or two about engineering and how to deal with aging robotics on a planet tens of millions of miles away.

The biggest age-related challenge currently isn't the rover's failing instrumentation or freezing wheel actuators, it's actually the rover's flash memory. Not designed for a multi-year mission, Opportunity's flash memory (akin to a computer's hard drive) is becoming worn out and NASA engineers have been working on strategies to bypass damaged memory banks, instead relying on the rover's on-board volatile memory (i.e. similar to a computer's RAM, which doesn't store data for long).

PHOTOS: 12 Years On Mars: Opportunity's Top 5 Revelations

Despite obvious limitations in what Opportunity can accomplish, valuable science is still being done. Most recently, the rover used its rock abrasion tool attached to its robotic arm to scrub a circle in the surface of a rock dubbed "Private John Potts" in "Marathon Valley," a location so-named for being Opportunity's "finishing line" when it completed just over 26 miles driven since landing in 2004. With the surface of the rock removed, other instruments on its robotic arm can be used to study its composition and therefore help geologists understand the conditions in which the rock was formed.

Marathon Valley is located in Endeavor Crater's rim, a crater the rover has been exploring since 2011. Orbital observations show the Valley has interesting clay deposits (formed when the Martian environment was a lot wetter than it is now) that Opportunity is investigating.

"With healthy power levels, we are looking forward to completing the work in Marathon Valley this year and continuing onward with Opportunity," Callas concluded.

It may be fighting age-related issues, but Opportunity certainly isn't done with Mars yet.

The target beneath the tool turret at the end of the rover's robotic arm in this image from NASA's Mars Exploration Rover Opportunity is "Private John Potts."

NASA's Mars Exploration Rover Opportunity was designed to last just 90 days on Mars. Today, on Jan. 25, it is celebrating

12 years

of working on the Red Planet's surface. Though the rover is showing inevitable signs of age,

such as flash memory problems

, it is still taking valuable observations and measurements of the Martian surface. Here is a


small selection some of the things it has done since landing at Meridiani Planum in 2004.

MORE: Drive With Opportunity on Epic Mars Rover Marathon

Photo: A simulated view of Opportunity overlaid onto an observation of the Martian surface made by the rover.

While Opportunity was not equipped to look for life itself, it can look for the conditions of habitability for life in the past. One of those key elements is water, and Opportunity was lucky enough to stumble upon signs of it shortly after landing in 2004. It found concretions of "blueberries" made of hematite, an element that generally forms in the presence of water. It also found evidence of jarosite, which is created in acidic water. Later in its mission, Opportunity found crossbeds -- small centimeter-size rock layers that overlap each other and show that water once flowed through the area.

MORE: Mars Rover Opportunity Suffers Worrying Bouts of 'Amnesia'

Photo: This false-color image taken by Opportunity on Mars shows concretions, nicknamed "blueberries", that formed in the presence of water.

The challenge with Mars is we've only sampled a few locations up close, the majority of our observations from afar, in orbit. This makes it hard to answer questions such as how abundant methane is, because different instruments have recorded wildly different measurements of the molecule (which in some cases points to life processes). One of Opportunity's notable discoveries in this area was helping to create the first atmospheric temperature profile, in concert with NASA's Mars Global Surveyor (a mission that is no longer operating today). This showed how warm different layers of the atmosphere are at that one location, which gave a snapshot of Mars' global weather. Several atmospheric science papers have also been published.

MORE: Watching the Sunsets of Mars Through Robot Eyes

Photo: Cirrus clouds spotted by Opportunity in November 2004.

While seeking out the past and present habitable conditions remains the key focus of Martian exploration, we are also interested in other parts of its geology. How long ago did the volcanoes erupt? When were craters formed? What were the conditions that created various rocks on the surface? By comparing with Earth and running models of Martian climate, we can then begin to reconstruct the planet's past. Opportunity's major geological discoveries were water-related, specifically finding the elements hematite and jarosite on Mars. The rover also sends back hundreds of pictures a week of geological features, which are used for long-term studies to build up our understanding of the Red Planet.

MORE: Rover Opportunity Has Found Some Odd Mars Rocks

Photo: Opportunity's robotic arm stretches towards a rock dubbed "Tisdale 2" in 2011.

Opportunity was not built to do astronomical observations per se, but it has looked up into the night sky from time to time. One recent prominent example was when Comet Siding Spring came within just 87,000 miles (139,500 kilometers) of Mars. Along with a fleet of other Mars spacecraft, Opportunity took pictures of the celestial visitor to get more information about how comets look and behave. The rover has additionally been used to watch the Martian moons, Phobos and Deimos, transit across the sun. The Earth is also highly visible in the rover's camera.

MORE: NASA Spacecraft's Epic 10 Years of Mars

Photo: Opportunity's view of Comet Siding Spring, which passed close to Mars in 2014.

When the rovers headed out to Mars, NASA was pursuing a Constellation program that was intended to put humans on the Red Planet around the 2030s. While the program was cancelled, NASA maintains that its Orion spacecraft today is still preparing humans for working on the Red Planet. A large part of that will be problem-solving, as was demonstrated in the 2015 movie "The Martian." It's well-known that Opportunity's twin rover, Spirit, died in a sand trap. But Opportunity also got stuck in the sand for a month and with NASA's help, successfully escaped. Engineering information from the Mars rovers is also telling scientists about how well wheels perform in the soil, how lubricants do in very cold temperatures, and the performance of solar panels.

MORE: 12 Years On Mars: Opportunity's First Sols

Photo: A scene from the 2015 movie "The Martian."